Chemical fixation and solidification processes have found recent favor for detoxifying hazardous waste materials and for producing solid waste having physical properties suitable for ultimate disposal in landfills, ocean dumping, and the like. Part of the impetus for developing new methods of chemical fixation and solidification has arisen from the hazardous waste control program called for under the Resource Conservation and Recovery Act of 1976 (RCRA), Public Law 94-580, which charges the United States Environmental Protection Agency with the responsibility for implementing and supervising the hazardous waste control program. Under that program, promulgated in 1980, a series of regulations issued which required that certain sludges, slurries and other liquid wastes containing specified hazardous materials may no longer be deposited in landfills without pre-treatment, stabilization, and dewatering. Wastes must additionally have acceptable toxicity levels as measured by certain established tests before they can be discarded in a landfill.
One primary objective of these governmental regulations is to achieve a non-flowing consistency of the wastes by reduction of the liquid content or increase of the solid content to eliminate the presence of free liquids prior to final disposal and a landfill.
Various waste solidification methods are known in the art. For example, U.S. Pat. No. 3,837,872 discloses a method for treating liquid wastes by adding an aqueous solution of an alkali metal silicate and a silicate setting agent, which converts the waste into a chemically and physically stable solid product. The patent to Thomson, U.S. Pat. No. 3,980,558, discloses a method for treating liquid wastes by adding a solidification agent consisting essentially of hydraulic cement. Abandoned application Ser. No. 510,152 of the present applicant discloses a method for treating aqueous liquid and semi-liquid wastes by solidification by mixing the waste with a dry water-reactive solidification agent comprising cement, a dry water absorbent material, and a powdered alkali metal silicate to convert the admixture into a chemically and physically stable end product which contains virtually no free-standing water.
If a particular waste cannot be detoxified even though solidified, it requires disposal in a secure landfill where landfill liners and leachate collection systems protect the groundwater in the vicinity of the landfill from contamination by the wastes. The efficacy of such landfill liners and leachate collection systems is enhanced if the wastes are encapsulated during or immediately after treatment and prior to disposal in the landfill, since encapsulated wastes are less likely to release hazardous substances into the groundwater. In some cases, encapsulation is accomplished by pouring the wastes while still liquid into an impermeable plastic bag or other similar disposable container which holds the waste while solidification is occurring. The waste is then transported in the containers to the landfill where the waste and container are buried.
There are several advantages to containerizing wastes in addition to the improvement in the operation of secure landfills. For example, if a waste has an offensive odor, even when the waste has been detoxified the handling, transportion, and disposal of the waste becomes a problem. Containerizing or encapsulating such wastes in plastic or other similar impermeable material minimizes problems due to odor and in many cases completely prevents odors from occurring.
Encapsulated or containerized wastes provide the additional advantage that such containerized wastes present a better appearance to neighbors of a landfill and therefore help prevent problems with public acceptance. Moreover, for wastes which even when solidified are not sufficiently detoxified to allow disposal in a nonsecure landfill, the encapsulation or packaging of the waste in an impermeable container provides an extra level of safety by assisting in the prevention of the formation of toxic leachate from the wastes in a secure landfill.
Even when wastes are solidified, wastes can sometimes produce dust particles which can separate from the solidified wastes during transportion, as for example when solidified wastes are carried in a dump truck. Accordingly, environmental regulations require a plastic liner for sealing the top of the truck. Certain types of waste which are particularly noxious require seals over transportation containers even if the waste does not produce dust particles when transported. Containerizing these wastes would meet these environmental requirements as a matter of course.
When a waste is in a liquid or semi-liquid form and is to be treated by solidification, it is usually necessary to place the waste in some form of container while it hardens. Various types of containers have been developed for use in the waste solidification industry and generally are inexpensive and readily available. A problem sometimes arises however in removing the solidified wastes from the containers for transportion and landfilling. Plastic liners have been proposed for the waste solidification containers so that the wastes will be easily removable after solidification. Sometimes, these liners do not work as well as would be liked because of the fact that the solidifed waste is a large, monolithic block and the containers are typically of unitary construction and frictionally resist removal of the block. Casting the waste into smaller containers for transportation to the disposal site has been demonstrated to work better than casting into a large block, but it is inefficient and expensive since it increases the cost of containerizing per unit volume of waste disposed of. Additionally, large monolithic waste blocks are sometimes difficult to handle with conventional landfill operating equipment because of the hardness of the waste.
Accordingly, there has long been a need for an efficient and effective method for containerizing or encapsulating toxic and nontoxic liquid and semi-liquid wastes which are treated by solidification.